Meftal P (Mefenamic acid) is generally safe for treating fever in children, though Paracetamol is usually the preferred first-line option. Since your brother has already taken a half tablet, he should be fine. However, ensure he took it with food or milk to prevent stomach upset. Do not give him any further doses without consulting a pediatrician, as the safe dose depends strictly on his specific weight and age. Monitor him for any side effects like stomach pain, nausea, or skin rashes. If his fever remains high or he feels unwell, please consult a doctor immediately.